The raid 0.9 does readbalancing but Mika's patch refines reads further.
See http://www.icon.fi/~mak/ for information on the patch but in my experience it
speeds up reads on raid1.
Godfrey Livingstone
Andrea Arcangeli wrote:
> On Tue, Dec 19, 2000 at 12:16:03PM +0100, Holger Kiehl wrote:
> > Does it also include the raid1 readbalance patch from Mika?
>
> it seems raid code in 2.2.18aa2 does rebalancing during reads in raid1:
>
> /*
> * read balancing logic:
> */
> mirror = conf->mirrors + last_used;
> bh->b_rdev = mirror->dev;
> sectors = bh->b_size >> 9;
>
> if (bh->b_blocknr * sectors == conf->next_sect) {
> conf->sect_count += sectors;
> if (conf->sect_count >= mirror->sect_limit)
> switch_disks = 1;
> } else
> switch_disks = 1;
> conf->next_sect = (bh->b_blocknr + 1) * sectors;
> /*
> * Do not switch disks if full resync is in progress ...
> */
> if (switch_disks && !conf->resync_mirrors) {
> conf->sect_count = 0;
> last_used = conf->last_used = mirror->next;
> /*
> * Do not switch to write-only disks ...
> * reconstruction is in progress
> */
> while (conf->mirrors[last_used].write_only)
> conf->last_used = conf->mirrors[last_used].next;
> }
> bh_req = &r1_bh->bh_req;
> memcpy(bh_req, bh, sizeof(*bh));
> bh_req->b_end_io = raid1_end_request;
> bh_req->b_dev_id = r1_bh;
> map_and_make_request (rw, bh_req);
> return 0;
>
> Of course you can't do rebalancing during writes.
>
> Is Mika's patch more advanced than the above?
>
> > And why is the 'shared' value of free or /proc/meminfo always 0. Under
> > plain 2.2.18 this is not the case. I saw this under aa1 and aa2.
>
> And you will see this under 2.4.0 too ;). It will avoid to lose clock ticks and
> latency loss while reading /proc/meminfo if you have some good ram (starting
> from 256M). On a 9G alpha machine xosview rended the machine kind of unusable
> due such evil O(N) loop ;).
>
> Andrea
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